Thunderstorms are already ongoing this morning from eastern Nebraska through Wisconsin and into western Upper Michigan, supported by a strong low-level jet transporting warmer and more humid air northward. These storms should gradually lift northeast and weaken through the morning. Across Wisconsin and Upper Michigan, lingering clouds and rain from this morning’s activity should also limit how unstable the atmosphere can become later today, keeping the overall severe weather threat fairly low.
There is a little more uncertainty across Minnesota this afternoon as a cold front begins pushing east across the region. Some instability may develop ahead of the front, and there will be plenty of wind shear available to support organized thunderstorms. The biggest question is whether storms can actually develop, as a layer of warmer air aloft may keep the atmosphere capped. If a few storms can break through that cap and become established, they could become strong or severe, but storm coverage is expected to be limited.
The more organized thunderstorm threat should develop farther south from Iowa into eastern and southern Nebraska and northern Kansas later this afternoon and evening. Stronger sunshine and daytime heating will combine with dew points in the 60s and 70s to build a moderately to strongly unstable atmosphere, with CAPE potentially reaching 2,000–3,000 J/kg. Thunderstorms should begin developing as the advancing cold front encounters this increasingly warm, humid and unstable air mass.
Wind shear will be strong enough to organize these storms, although the overall setup favors storms quickly growing into broken lines and clusters rather than remaining as isolated supercells. That should make damaging wind gusts the primary severe weather concern from the middle of the afternoon into the evening. The low-level jet will strengthen again this evening from western Kansas into central Iowa, increasing low-level wind shear and introducing a low tornado risk. However, storms are expected to become increasingly outflow-dominant or elevated with time, which should keep the tornado threat relatively limited. Overall, damaging winds with scattered strong to severe thunderstorms will be the primary concern from northern Kansas and eastern Nebraska into Iowa later today.